A conventional motion transmission system comprises, in the rear part of the bicycle, a wheel equipped with a hub comprising a body element, in the jargon known as “freewheel body,” capable of rotating idly with respect to the hub in one direction of rotation and of making it rotate in the opposite direction.
The freewheel body is generally cylindrical with outer grooves adapted to engage the sprockets of a sprocket assembly. The sprockets in turn are engaged and made to rotate by a chain, which receives the movement from at least one guide toothed wheel associated with a crank arm. This entire assembly can be heavy and in an effort to reduce this weight, some lighter designs can be weak.